title: Metabolism of angiotensin-(1-7) by angiotensin-converting enzyme.
abstract: Angiotensin converting enzyme (ACE) inhibitors augment circulating levels of the vasodilator peptide angiotensin-(1-7) [Ang-(1-7)] in man and animals. Increased concentrations of the peptide may contribute to the antihypertensive effects associated with ACE inhibitors. The rise in Ang-(1-7) following ACE inhibition may result from increased production of the peptide or inhibition of the metabolism of Ang-(1-7)-similar to that observed for bradykinin. To address the latter possibility, we determined whether Ang-(1-7) is a substrate for ACE in vitro. In a pulmonary membrane preparation, the ACE inhibitor lisinopril attenuated the metabolism of low concentrations of 125I-Ang-(1-7). The primary product of 125I-Ang-(1-7) metabolism was identified as Ang-(1-5). Using affinity-purified ACE from canine lung, HPLC separation and amino acid analysis revealed that ACE functioned as a dipeptidyl carboxypeptidase cleaving Ang-(1-7) to the pentapeptide Ang-(1-5). The ACE inhibitors lisinopril and enalaprilat (1 micromol/L), as well as the chelating agents EDTA, o-phenanthroline, and DTT (0.1-1 mmol/L) abolished the generation of Ang-(1-5) and did not yield other metabolic products. Ang-(1-5) was not further hydrolyzed by ACE. Kinetic analysis of the hydrolysis of Ang-(1-7) by ACE revealed a substrate affinity of 0.81 micromol/L and maximal velocity of 0.65 micromols min(-1) mg(-1). The calculated turnover constant for the peptide was 1.8 sec(-1) with a catalytic efficiency (Kcat/Km) of 2200 sec(-1) mmol/L(-1). These findings suggest that increased levels of Ang-(1-7) following ACE inhibition may be due, in part, to decreased metabolism of the peptide.
authors.affiliation: Hypertension Center, Bowman Gray School of Medicine, Wake Forest University, Winston-Salem, North Carolina 27157-1095, USA. mchappel@bgsm.edu
authors.forename: M C
authors.initials: MC
authors.lastname: Chappell
authors.forename: N T
authors.initials: NT
authors.lastname: Pirro
authors.forename: A
authors.initials: A
authors.lastname: Sykes
authors.forename: C M
authors.initials: CM
authors.lastname: Ferrario
mesh_terms: D000803:Angiotensin I; D000804:Angiotensin II / Q000378:metabolism*; D000806:Angiotensin-Converting Enzyme Inhibitors / Q000494:pharmacology; D000818:Animals; D001920:Bradykinin / Q000378:metabolism; D002462:Cell Membrane / Q000201:enzymology; D004285:Dogs; D006801:Humans; D007700:Kinetics; D017706:Lisinopril / Q000494:pharmacology; D008168:Lung / Q000201:enzymology*; D008956:Models, Chemical; D010446:Peptide Fragments / Q000378:metabolism*; D007703:Peptidyl-Dipeptidase A / Q000378:metabolism*
chemical_list: D000806:Angiotensin-Converting Enzyme Inhibitors; D010446:Peptide Fragments; D000804:Angiotensin II; D000803:Angiotensin I; D017706:Lisinopril; D007703:Peptidyl-Dipeptidase A; C118790:angiotensin I (1-7); D001920:Bradykinin